Thermal Effects on Energy Consumption and Range

Looking at energy consumption, right off the bat, we can see that cold weather has a significant impact on EC - nearly double in urban driving, 40% more in the highway cycle, and 25% on the US06. It’s worth noting here: the Leaf has an 80 kW electric motor, a 24 kWh battery, and a 5 kW resistive heating element.

When broken down further, into a base load case (driving cycle EC at 72F), the amount of extra energy needed to drive the cycle at 20F (listed as EC cold), and then the heater load required to maintain a cabin temperature of 72F, we can see that a significant portion of the additional energy consumption is down to the heater. As with most gasoline cars, driving in sub-freezing temperatures only makes the car about 10% less efficient before heater loads are considered. The mechanically-driven heating elements in conventional vehicles add another 5% or so in terms of mechanical efficiency loss, while obviously the electric heater in the EV is far more costly from an energy consumption standpoint even though it doesn’t increase mechanical losses at all.

(Note: graphs were created by ANL using the raw 10Hz data instead of the filtered 1Hz data available on D3. Available as part of APRF's AVTA Nissan Leaf testing analysis and summary, as presented by Dr. Henning Lohse-Busch. Full presentation available here.)

And while energy consumption is a big deal, range is the be-all, end-all concern for most consumers. With the heater on, that’s a decrease in range by anywhere from 20-50% depending on your drive cycle. That’s a lot. And you can just look at the APRF’s full charge tests at 20F and 72F to see what I mean: 

Think about that - this is a car that, at launch, Nissan claimed had a 100 mile range. My own real-world driving suggests 80-85 a decent estimate. EPA says that number is closer to 73. The APRF’s instrumented testing backs that up (74.1 mile range at 72F), but the same instrumented testing, in 20F weather? 46 miles. That’s it. 

Introduction and Technology Background How this Impacts the Model S & Final Thoughts
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  • wetwareinterface - Tuesday, February 19, 2013 - link

    top gear did a hatchet job???

    they said the car performed well with great accelleration and a fast top speed. handling wasn't as good as the lotus the car is based off of. range when driving fast was also dreadful.

    overall they said the car was pointless given that it cost more than the lotus, had only marginally better accelleration and top end, and would stop after 55 miles of hard driving and require 8-12 hours of recharging.

    the fact is the tesla roadster is a bad idea all around and is only for the ultra rich to collect and use as a toy on short runs.

    the tesla s also has abysmal range in cold weather, and takes a along time to charge. it's completely unusable for an only car based on range alone. you might as well state that the tesla's 311 miles is the max driving per day given the recharge time.

    when they make hydrogen cars a reality and store electricity as said hydrogen instead of in a battery then a car that runs off the grid will make sense. until then unless there's a huge leap forward in battery technology we won't see a practical electric vehicle.
    Reply
  • Aikouka - Wednesday, February 20, 2013 - link

    That link is the exact reason why I asked.

    I remember when the Top Gear lawsuit first became news, and I gave Tesla a fair shot with it. Since the segment happened a bit prior to the news, I had to rewatch it to properly form my opinion. Honestly, I couldn't see what Musk was belly aching over. Probably the first 75% of the review was praising the upsides versus a petroleum-based vehicle, and the latter portion was discussing the downsides (range and charge time).

    After this latest issue, it's pretty obvious that Musk needs a few lessons in being a company figurehead.
    Reply
  • Beaver M. - Tuesday, February 19, 2013 - link

    But its true!
    Ive driven one myself and it is 100% true that the batteries dont last very long if driven like a sportscar! It also had quite a few other quality issues.
    Reply
  • Death666Angel - Tuesday, February 19, 2013 - link

    Duh. The suite was dropped by the judge btw. The show was scripted and edited in a way to provide entertainment but nothing they states was untrue. Reply
  • JPWhite - Tuesday, February 19, 2013 - link

    It's only libel if it's not true. Reply
  • othercents - Monday, February 18, 2013 - link

    I think we should be looking at changing car testing now since obviously there has been significant discrepancy in multiple vehicle MPG tests and I don't think they correctly reflect real world driving compared to older vehicles. In the past you could count on a 2-4MPG difference between tested MPG rating and real world, however now I have see as much as 20MPG difference which if properly informed a buyer might choose a different vehicle with lower tested MPG, but gets better real world MPG. Reply
  • blowfish - Monday, February 18, 2013 - link

    Good article, Vivek, and the more so coming from an actual EV user.

    The fact remains that people are obsessed about range - whereas most commutes are only a few miles, and so even the 46 mile range of the Leaf in worst case conditions is more than adequate. For longer trips, maybe a charging trailer equipped with a generator would be the way forward until such time as battery technology has improved.

    Sadly, most drivers are probably unable to adapt their driving styles. Every day, I see folks flooring it between stoplights, rather than driving at the appropriate speed so as to get the "green wave". Those who do try to drive sensibly find others cutting in front of them, desperate to gain those one or two places that are evidently such an important part of their lives....

    The real way forward for shorter commutes, however, is for people to get on their bikes, and get healthy as a side benefit. Here in Louisiana, however, cyclists are often assumed to be people who can't afford cars, and regarded as a nuisance by most drivers, and when you ride a bike on the road, you are aware that you are risking your life.
    Reply
  • Guspaz - Monday, February 18, 2013 - link

    Models of the Nissan Leaf sold in cold-weather countries like Canada feature various changes to function better in low temperatures. One example is that the Canadian model comes with a battery heater to improve efficiency at low temperatures, while the US model, to my knowledge, does not.

    It's not really fair to test the US model of the Nissan Leaf in cold temperatures. One of the cold-weather models should have been tested instead.
    Reply
  • bobbozzo - Monday, February 18, 2013 - link

    20F is not very cold.

    It was 27F in southern California recently, in the LA metro area.
    In the mountains would be even colder.

    Also, it gets below 0F MANY places in the US.
    Reply
  • cmart - Tuesday, February 19, 2013 - link

    Gets? It stayed below zero, day and night, for eight days here recently (Northern Minnesota). Reply

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